For the last year, I've been getting CEL P0300, P0303, P0301 and P0305 cylinder misfire codes. They usually stay on anywhere from a day or two to less than an hour and then go away. Lately they've been coming on more regularly and staying on longer. Most recent was P0300 and P0420 which I reset a couple days ago and today I have P0420 back. My question is do you guys think the P0420 is being caused by the cylinder misfire codes? What should I look into for this issue? I'm not a gearhead but would like to get some thoughts and input. I have a mechanic who lets me buy my own parts and he charges labor for installation so just wondering what parts I should look into. I alreay have three brand new OEM ignition coils sitting around...should I replace them in the troubled cylinders? That might take care of the cylinder misfire codes but would that also affect P0420?

 

Misfire codes not related to the P420. You have two different problems.

If you haven't yet change out your spark plugs. Then you can see if that helps on the misfire codes. If that doesn't work then change the ignition coils. Once you get those codes taken care of you can focus on the P0420.

You can do a search on P0420 code...plenty of info on this website.

 

Cool, I've changed spark plugs so I don't think they're the issue. I've had P0304 before and after changing cylinder 4 ignition coil, code went away. I will look into changing bank 1, 3 and 5 coils since they are hard to get to and so I might as well get them all done at once. I assume the coils can be tested to see if they are good or bad?

 

If you run a misfire for a while it destroys your cats hence the p0420

Replace your coils

 

True, but symptom wise they are unrelated.

 

Yeah if you have an 02 or 03 you have to remove intake manifold. Might as well change both your plugs and ignition coils.

 

I think 01, 03 and 05 are the ones where you have to remove intake manifold. 02, 04 and 06 are easy to get to.

 

this is correct. 1,3 & 5 are along the firewall, hidden under the intake manifold.
Cyls 2,4 & 6 are by the radiator, very easy to get to.

 

I have seen it once on a 4cyl the cat was so clogged it misfired. I do not recall if it threw the code though.

Kind of odd its the rear bank that is misfiring though?

 

Not really because those codes are not related....typically, although in rare cases such as what you mention they can be related. Very unlikely in his case...

 

Negative ghost rider.


VQ30DEK (2000-2001) All coils are accessible without IM removal. Only the TB cables and bracket are in the way.


VQ35 (2002-current) Require IM to be removed to access the rear three cylinders.


OP never stated which motor/year maxima he's working on.

 

I'm running an 03.

 

My 01 requires removal of the intake manifold..?

 

I would go ahead and replace all three (cyls 1 5 3) coils with OEM replacements from the dealer. Since you already have replaced the plugs, you know what it takes to get the IM off.....and you already have new coils. I think you were headed in that direction already.


Since you have the thing pulled apart, you might as well look into what NWP has to offer.

 

What?


No.


I think you're confused brother. Maybe reread that sir.

 

No sir, i had to inspect the rear ones a few months ago and you do have to remove the intake manifold to access the coils closer to the firewall. The front bank is accessible in a matter of seconds.

 

Okay, lets make sure we are talking about the same engine here.


If you have a VQ30DEK motor in your 2000-2001 Nissan Maxima, the coils are accessible WITHOUT removing the intake manifold.


If you have a VQ35 motor in your 2002-current I.E. 2014 Nissan Maxima, the intake manifold MUST be removed to get to the rear, firewall side, coils/plugs.


I am not wrong.

 

Well in an effort to prove myself, I went out to my car (2001) and you are correct. The one I worked on a few months ago was a friends.. he said it was an 01 BUT I ran over to his house just a second ago and its an 02 BUT it had been in an accident and has 01 headlights and bumper rigged on there with nails and screws. My apologies:\_

 

No worries. No need to apologize man.


I respect your effort to prove yourself. I have done similar things haha.


Nails and screws? Damn. Does he ever exceed the posted speed limit?

 

Thanks for being chill about it.
Did I mention duct tape?
And no he drives like an idiot and he showed me where he 'got bored' and added more slits in the backs of his seats with a knife -___- such a sad maxima

 

Quick follow-up on this. If the issue was my O2 sensor, is that a separate code? Or could/would the O2 sensor cause this code?

My CEL went away couple days ago.

 

Yup, that sounds consistent with other people who show a P0420 or P0430 code. Ultimately, it comes down to either the primary O2 sensors (have to change both) or the specific pre-cat for that code.

P0420 = rear pre-cat (closer to the firewall), bank 1
P0430 = front pre-cat (closer to the front of car), bank 2

If you are experiencing any misfire codes you need to take care of those first and foremost.

 

^ +1


Deal with the misfires first. Clear codes.


If you have a scanner, you can watch the O2 voltages in real time.


If they are indeed bad, replace the primary (upstream) sensors and sim the (downstream) secondary's. I think the new sims even take care of the heaters too.

 

Ack..correction to my last post. You would possibly need to replace BOTH downstream (secondary) O2 sensors for a P0420.

Or, you can install O2 sims if you don't want to replace the O2 sensors or deal with the cat. If you do this option it is probably best to punch out the cat or install an aftermarket y-pipe to eliminate the rear pre-cat.

 

Thanks, what am I looking for as far as the O2 voltage? What is a sim? I have the TorquePro app for Android and will see if it provides O2 sensor information.

Also, do shops have a way/equipment to test ignition coils and O2 sensors to see if they're good/bad?

Lastly, I assume a bad O2 sensor would generate misfire codes on random cylinders. I've been getting the cylinder misfire codes consistently on cylinders 3 and 5. Would that make it more likely that the issue is just the ignition coils and not the O2 sensors?